Device for continuous liquefaction of siliceous material

ABSTRACT

An apparatus and method for the continuous liquefaction of finely divided raw material capable of forming a highly viscous material when heated to molten condition, the apparatus including a hollow vessel, means for constricting the bottom opening of the vessel, means for adding the finely divided material into the vessel at the same time the viscous material is removed through the bottom opening of the vessel, a pair of horizontally disposed electrodes in the vessel for producing an electrical arc to generate sufficient heat to form a molten viscous melt from the raw material, and means for removing the molten viscous melt from the vessel at substantially the same rate as the melt is formed for maintaining a stable condition within the vessel. The disclosed method continuously forms a viscous extrusion melt from finely divided raw material which is charged into the vessel, the melt being withdrawn by gravity or by rollers and broken or severed periodically. The conversion of silica i.e. sand into fused silica is disclosed.

United States Patent Niwa et al.

1451 Sept. 5, 1972 [54] DEVICE FOR CONTINUOUS LIQUEFACTION OF SILICEOUSMATERIAL [72] Inventors: Shohei Niwa, Mizunami; Kazuo Oki,

Okazaki; Masaaki Hayashi, Nagoya; Yuukichi Morimoto, Kariya, all ofJapan v [73] Assignee: Glasrock Products, Inc.,

22 Filed: March 8,1971 21 Appl.No.: 121,974

Atlanta,

[30] Foreign Application Priority Data March 12, 1970 .lapan ..45/20660July 2, 1970 Japan ..4s/57s47 [52] US. Cl. ..13/6, 65/324, 65/327,-65/347, 65/356 [51] Int. Cl. ..C03b 5/02, C03b 17/00 [58] Field ofSearch 1 3/6, 9; 65/18, 347, 356, 325, 65/326, 327, 324

[56] References Cited UNITED STATES PATENTS 10/1963 Silverman 6 /347 UX9/1964 De Bussy ..l3/6

FOREIGN PATENTS OR APPLICATIONS 400,472 10/1933 Great Britain 1 3/6Primary Examiner-Roy N. Envall, Jr. Attorney-Douglas M. Clarkson [57]ABSTRACT An apparatus and method for the continuous liquefaction offinely divided raw material capable of forming a highly viscous materialwhen heated to molten condition, the apparatus including a hollowvessel, means for constricting the bottom opening of the vessel, meansfor adding the finely divided material into the vessel at the same timethe viscous material is removed through the bottom opening of thevessel, a pair of horizontally disposed electrodes in the vessel forproducing an electrical arc to generate sufficient heat to form a moltenviscous melt from the raw material, and means for removing the moltenviscous melt from the vessel at substantially the same rate as the meltis formed for maintaining a stable condition within the vessel. Thedisclosed method continuously forms a viscous extrusion melt from finelydivided raw material which is charged into the vessel, the melt beingwithdrawn by gravity or by rollers and broken or severed periodically.The conversion of silica i.e. sand into fused silica is disclosed.

44 Claims, 16 Drawing Figures PAIENTED SE? 5 I972 I SHEET 3 0F 6 FIG 4FIG 3 PATENTEDSEP 51912 SHEEI 6 [IF 6 DEVICE FOR CONTINUOUS LIQUEFACTIONOF SILICEOUS MATERIAL BACKGROUND OF THE INVENTION Fused silica (alsoknown as amorphous silica, silica glass or quartz glass) in finelydivided form, as a raw material has recently been demanded in largequantities. Devices for preparing fused silica have been developed inthe past. Such prior art devices comprising carbon electrodes, disposedin the center of a housing, charged with granular or powdered siliceousmaterial, such as sand. Current, passed through the electrodes, producedan electrical arc which generated sufficient heat to permit the materialsurrounding the electrodes to be melted into a hollow globe-like melt.The current was then turned off and the globe removed from the housingby various means, such as by inverting the housing.

The melt would then be allowed to cool. As it cooled, the variousimpurities and contaminants in the melt, such as iron, oxides of iron,alkali metals, oxides of alkali metals, silicates, aluminum compounds,and titanium compounds, being more mobile than the fused siliceousmaterial, would tend to be concentrated in the cooler area around theoutside of the surface of the melt. As a result, a contaminated skinwould form around the cool fused siliceous material which requiredremoval before further work could be done on the melt. The skin wasremoved by a peeler stripping or hammering away at the skin and, ineffect, peeling the skin from the surface of the melt.

Once the skin was removed, the fused silica would then be comminuted toa granular, powdered or finely divided state and used according to itspurity. Meanwhile, the obviously non-continuous method of producing thefused silica melt would be carried out, again. Unused sand from theprevious melt would be recycled and used with the new batch of sand,thus trapping a higher concentration of impurities from the old sandwith the new sand. The resultant melts would then have thicker skins tobe peeled off.

This old batch process had still other drawbacks, such as a highelectrical power consumption, necessitated by the requirement togenerate an electrical arc of sufficient intensity to heat to fusiontemperature each batch of raw material. Since there was never anyconservation of this heat, from one batch production of the melt to thenext, the electrical power consumption was, in turn, very high. Also,the amount of fused silica produced by this old method and apparatus wasinefficiently small. Another drawback was that, since the electrodeswere not continually generating an electrical arc, there was a highconsumption of these electrodes since they were heated and cooled duringeach cycle intermittently. US. Pat. No. 3,151,964 discloses the oldprocess discussed above.

A method of continuously preparing fused silica by flowing the meltdownwardly through extrusion nozzles was disclosed in the British Pat.No; 400,472. However this method of continuous liquefaction has had nopractical application because of the extreme difficulty in maintaining astable furnace situation. This situation is due mainly to the extremelyunstable environment in the arc generating section of the furnace. Thedetermining factors in the stabilization of the furnace situation havenot yet been clarified. Probably these factors are viscosity,temperature, etc. as for the raw material, and current, voltage,electrodes, etc. for the temperature. Also, there is the relationshipbetween the amount of extruded melt and the supply of raw material.

SUMMARY OF THE INVENTION Briefly described, the apparatus of the presentinvention included a furnace or vessel having a hollow cylindrical,water jacketed body, the bottom wall portion being frusto-conical, andtapering abruptly inwardly and downwardly from the lower edge of thecylindrical body to terminate in a depending hollow cylindricaldischarge nozzle, which is also water jacketed. An annular throatdefining lip of refractory material, is retained by and forms a liningfor the nozzle. Below the nozzle, in removable coaxial abuttingrelationship thereto, is a tubular, water jacketed, solidificationsleeve which provides a cooling passageway, through which the moltenmaterial passes. A hood or cover for the escape of gases generated bythe electric arc is disposed over the upper end of the body and a rawmaterial make up conveyor, for maintaining an appropriate level of rawmaterial in the body of the furnace, feeds into a chute connected to thehood.

For temporarily closing the open bottom of the fur nace, so that aninitial charge of granular or powdered raw material can be received andmelted sufficiently to form a seal against the annular lip, isa cupshaped bottom cap provided with a gate type bleeder valve. The bottomcap is carried on a vertically moveable elevator which holds the cap inplace for the initial start up and bleeding of raw material from thefurnace sufficiently for the molten melt seal at the throat. Thereafter,the elevator alone may provide support for the lower end of thegradually descending molten column of viscous material passing from thenozzle through the sleeve.

In a second embodiment of the invention, opposed endless primaryconveyors, having various surface configurations, are substituted forthe elevator and function, during the main run of the furnace, forgradually feeding the emerging column of molten material. An angledsecondary conveyor functions to break the column periodically and conveyaway the resulting product.

The method performed by the above apparatus include surrounding anelectric arc with siliceous raw material, such as sand, so as to createa globe of fused, molten, liquified viscous silica melt which graduallygrows, as the raw material is withdrawn from supporting the bottom ofthe globe through the restricted nozzle. Eventually, the liquified fusedsilica globe grows to such an extent that it seals off the throat of thenozzle, thereby preventing further discharge of the raw material bygravity from within the body of the furnace.

It is, therefore, a primary object of the present invention to providean apparatus and method for producing, in a continuous fashion, a fusedsilica product from siliceous raw material.

Another object of the present invention is to provide an apparatus andprocess of liquifying fuseable raw material which will reduce to aminimum the electricity consumption and increase the production rate.

Another object of the present invention is to provide an apparatus andprocess for producing fused silica which will result in an improvedproduct having essentially no contaminates and containing no skin whichmust be peeled from the product.

Another object of the present invention is to provide a process anapparatus for producing fused silica in which the contaminates areremoved during the production of the fused silica.

Another object of this invention is to provide a method and apparatusfor the continuous liquefaction of finely divided siliceous materialwhich produces a very high quality fused silica product.

Another object of this invention is to provide an apparatus for thecontinuous liquefaction of finely divided siliceous material which issimple in construction and use, economical to manufacture, and reliablein operation.

Still other objects features and advantages of the present inventionwill become apparent from the following description when taken inconjunction with the accompanying drawings of the illustrativeembodiments of the invention, wherein like reference charactersdesignate corresponding parts throughout the several views, and wherein:

BRIEF DESCRIPTION OF THE FIGURES OF DRAWINGS FIG. 1 is an explodedfragmentary prospective view of an apparatus constituted in accordancewith the present invention, certain parts being broken away for clarity;

FIG. 2 is a fragmentary side elevational view of the apparatus shown inFIG. 1, certain parts being broken away for clarity and having a matchline referring to FIG.

FIG. 3 is a fragmentary top plan view of the apparatus of FIG. 2;

FIG. 4 is a fragmentary end view of a portion of the apparatus shown inFIG. 2;

FIG. 5 is an side elevational view of the top portion or cover of theapparatus of FIG. 2 for disposition along the match line therein;

FIG. 6 is a schematic vertical sectional view on a reduced scale,showing a second embodiment of the apparatus of the present invention;

FIGS. 7 through 12 are enlarged side elevational views of variousextruding rollers which may be employed in the embodiment of FIG. 6; and

FIGS. 13 through 16 are schematic vertical sectional views of theapparatus of FIG. 1 through 4 in operation.

DETAILED DESCRIPTION OF THE DRAWINGS Referring now in detail to theembodiments chosen for the purpose of illustrating the presentinvention, and particularly to FIG. 2 thereof, it will be seen that aframe denoted generally by numeral 10 includes a plurality of upstandinglegs 11 which support the corners of a horizontal cooling sleevesupporting lower frame having longitudinally extending outer beams 12connected by transverse beams, such as beams 13 and 14. Spaced inwardlyfrom the longitudinal beams 12 are smaller longitudinal beams 15 whichare mounted on the horizontal frame, and are provided with transversebeams, such as beams 16. Spaced upstanding studs 17 on the subframeformed by the beams 15 and 16 support an upper frame which includeslongitudinal beams 18 which, in turn, are spaced apart by cross struts,such as struts l9.

Centrally located on the frame 10 is the furnace or fusion vessel,denoted generally by numeral 20. This fusion vessel includes a fusionchamber into which is charged the granular or powdered raw material Awhich is to be fused.

The furnace 20 includes a hollow cylindrical main body 21 having avertical axis. The upper end portion of body 21 is provided with aannular lifting ring 22 from which project four equally spaced liftingbrackets 23. The lower end of the body 21 is provided with an outwardlyprotruding annular flange 24 which abutts a complimentary flange 25 onthe bottom 26 of the fu' sion furnace 20. The bottom 26 is an invertedfrustoconical member which tapers downwardly and inwardly to terminatein a depending cylindrical nozzle 27.

The nozzle 27 projects a short distance downwardly and terminates in anannular, lip supporting, flange 28 which protrudes inwardly andoutwardly of nozzle 27 The inner peripheral portion of flange 28provides a supporting shoulder for an annular lip 29. This lip 29 isformed of a refractory material and is so dimensioned as to be snugglyreceived by the nozzle 27 to form a liner therefor, the upper edgeportion of the lip 29 tapering downwardly and inwardly with the sameslope and coinciding with the slope of the bottom 26 so as to formessentially an extension thereof. The lip 29 defines a throat or bottomopening for the nozzle, through which the molten or fused material, suchas fused silica G may flow during the fusion operation.

To protect the lip 29 from the intense heat of the fusion melt G, awater jacket is provided around the nozzle 27, the water jacket beingformed by the outer protruding portion of the flange 28 and anupstanding annular ring 30 ,which extends from the outer periphery offlange 28 to a position intermediate the inner and outer peripheries ofthe fusto-conical bottom 26. The water jacket 31 is thus defined by thenozzle 27 which forms the inner periphery of the jacket, the ring 30which forms the outer periphery thereof, the flange 28 which forms thebottom and a portion of the bottom 26 which forms the top. Suitableintake and outlet nipples 32 and 33 are provided for the circulation ofwater to and from the water chamber of jacket 31.

For cooling the main body 21, a similar water jacket is providedsurrounding the lower portion of body 21 this water jacket is defined byan annular ring 34 which is mounted on an annular channel 35 whichclamps the flanges 24 and 25 in their abutting relationship. The waterjacket is also defined by an upper annular plate 37 which protrudesinwardly from the upper edge of the ring 34 to an intermediate portionof the body 21. Suitable inlet and outlet nipples 38 and 39 provide forthe circulation of the water within the water jacket just described.

The opposed horizontally disposed electrodes 40 protrude through centralportions of the ring 34 and thence through the body 21 so as toterminate in the central portion of the fusion chamber defined by body21 in opposed aligned relationship. Annular insulation blocks 41 carriedby cylindrically shaped housings 42 surround the electrodes 40, theinner ends of the housings 42 abutting the outer surface of body 21 andthe peripheral portions of housings 42 being secured through holes inring 34, as illustrated in FIG. 1.

It will be understood that the electrodes 40 are capable of being movedinwardly and outwardly in an axial direction, i.e., a radial directionwith respect to the vertical axis of the furnace, so that the arc gapbetween the inner ends of the electrodes 40 may be varied, as desired.For this purpose, electrode carriers, denoted generally by numeral 50are provided on the frame 10, on opposite sides of the furnace 20. Eachcarrier 50 includes a carriage 51 which is provided with flanged wheels52 riding upon opposed longitudinally extending rails 53. The rails 53,in turn, are carried by upstanding brackets 54 on the beams 18.

Mounted on the central portion of the carriage 51 is electrode clampingassembly having opposed upper and lower clamping jaws 56 and 57. Theseclamping jaws are hingedly secured together along a common edge and arereleasably clamped by their other. edges by means of a crank mechanism58.

By movement of the carriage 51 inwardly and outwardly, the depth ofpenetration of the electrode 40 into the chamber defined by the body 21may be varied, as desired. For moving the carriage 51 inwardly andoutwardly with respect to the body 21, the lower portion of the carriageis provided with a rack 60 having downwardly opening teeth which meshwith a pinion 61 carried on a shaft 62 which shaft is journaled by thelongitudinally extending beams 18. Outwardly of the beam 18, shaft 62 isprovided with a pulley 63 driven by a belt 64 from apulley 65 on a gearreducer 66. To provide for very slow movement of the shaft 62, the gearreducer 66 is driven from a gear reducer 67 which, in turn, is driven bya motor 68 through belt 69. The gear reducers 66 and 67, as well as themotor 68 is mounted on beams 15, as best seen in FIGS. 2, 3 and 4.

Since the body 21 may be dumped periodically to permit the cleaning ofthe interior of the furnace and, particularly the cleaning of impuritiesfrom the bottom 26, the annular channel 35 carries substantially theentire weight of this body 21, the channel resting upon the beams 18 andthe central struts 19.

Below and coaxially aligned with the body 21 so as to receive and coolthe column C of fused silica or other melted viscous material, a cooleror cooling sleeve, denoted generally by numeral 70 is provided. In moredetail, this cooling sleeve includes a frusto-conical inner sleeve 71which diverges downwardly and outwardly, thereby providing an upperentrance opening 72 which is slightly smaller in diameter than the lowerexit openings 73 thereof. The upper entrance opening 72, however, is oflarger diameter than the throat of the lip 29 so that the upper edge 73aof the sleeve 71 abuts the bottom surface of flange 28.

The inner sleeve 71 is surrounded by outer cylindrical sleeve 74 whichis disposed concentrically with respect to sleeve 71 and is connectedthereto by upper annular wall 75 and lower annular wall 76. The sleeves71 and 74, together with the walls 75 and 76 define a water chamberthrough which a coolant is passed, the

outer cylindrical sleeve 74 being provided with nipples.

77 and 78 for. that purpose.

Four radially extending circumferentially evenly spaced channelshapedtrunnions 80 project outwardly from the outer sleeve 74 and areprovided with appropriategussets 81 for reinforcement. The outer ends ofthese trunions-80 carry blocks 82 from which project, downwardlyextending alignment pins 83 which are received in the upper ends ofbearing blocks 84. The bearing blocks, in turn, are carried by the transverse beams 13 and 14. It is therefore seen that when the body 21 isremoved from its position on the frame 10 the cooling sleeve is-free tobe lifted upwardly and out of the frame 10, as well.

As seen best in FIG. 1, below the cooling sleeve 70 is a cup shaped cap,denoted generally by numeral 90. This cup shapedcap is used only duringthe initial start-up of the furnace and may thereafter be dispensedwith. The cap 90, itself, includes an annular cylindrical body 91provided with a flat upper annular flange 92 and a flat lower annularflange 93. For convenience, the flanges 92 and 93 are L-shaped so thatthey may be readily secured to the cylindrical body 91. Verticallydisposed reinforcing ribs 94 are disposed circumferentially around theoutside surface of the body 91, these ribs 94 extending between theupper flange 92 and the lower flange 93 and being equally spaced apartcircumferentially.

The diameter of the body 91 is slightly larger than the diameter of theprotruding lower discharge end 73 of the inner sleeve 71 so that thisprotruding end portion may be received within the upper end portion ofthe body 91 in overlapping relationship.

The lower end of the body 91 is provided with a frusto-conical bottom 95which, like the bottom 26 tapers downwardly and inwardly to terminate inan annular discharge nozzle 96. The opening in discharge nozzle 96 isclosed by a gate valve which includes a radially mounted slideableplate97 seen best in FIG. 1. The plate 97 is carried by a rack 98secured to the nozzle 96. This rack 98 includes a flat plate carried bybot-' tom 96 and disposed above the slideable plate 97 the opposed edgesof the rack 98 being curved downwardly and then inwardly to define apair of opposed channel members receiving the edge portions of the plate97. A suitable handle 99, which protrudes radially outwardly of theplate. 97, permits manipulation of this plate so as to open and closethe nozzle 96, as desired.

Legs 100 project downwardly from the lower flange 98, the lower ends ofthe legs 100 being secured at the corners of a horizontally disposed capsupporting frame formed of longitudinally extending angle irons 101 andtransversely extending angle irons 102. This lower supporting framedefined by the angle irons 100, 101 is adapted to be carried by anelevator 105, shown in broken lines in FIGS. 1 and 2. Elevator 105 hasan appropriate opening 106, seen in FIG. 1 through which the sand or rawmaterial may flow, when the gate valve plate 97 is manipulated to opennozzle 96. The elevator 105 is provided with an appropriate support 107by means of which the elevator 105 may be manipulated in a vertical pathupwardly and downwardly.

The cap 90 is also provided with outwardly projecting radially spacedlugs 108 which are secured to the flange 93 to facilitate the handlingof the cap 90 so as to secure the same in place by means of chains (notshown) which may be wrapped around the frame 10.

For the purpose of venting gases generated by the electric arc duringthe fusion of the silica raw material, or like material, a hood or cover110, shown in FIG. 5, is disposed over the upper end of body 21. Thiscover has a cylindrical skirt 111 and a frusto-conical or truncatedfunnel 112 which leads from the skirt 111 to a discharge conduit 113.

Projecting through the funnel 1 12 of the cover 1 is a tubular chute 114which leads from a raw material storage bin 115. The raw material whichis fed by the conveyor 116 falls through the bin 115 and the chute 114into the interior of the body 21.

SECOND EMBODIMENT The numeral 201 designates a steel furnace body ofapproximately cubic box type. A furnace cover 203 disposed at the top ofthe body 201 is provided with a hopper 202 for feeding the powderedsiliceous material 204. A pair of bar graphite electrodes 205 arepositioned in alignment on both sides of the body 201. A suitablespacing is secured between the neighboring tips of the electrodes 205 sothat, when conducting, a sufficient electric arc is generated. Archeating in this case may be replaced by resistance heating. The barelectrodes 205 are supported by water-cooled insulators 206 andwater-cooled electrode holders 207 disposed on both sides of the body201 in such a manner that they are located horizontally andsymmetrically relative to the vertical body 201. The holders 207 arefixedly disposed on electrode-conveying devices 208 so as to allow themto move with respect to the stationary body 201.

A water-cooled steel nozzle 210 is positioned at the bottom of the body201. The bottom portions leading to the nozzle 210 are at an incline of15 to 55 degrees with respect to the vertical axis of the body 201 insuch a way that the melt 209 can easily be extruded through the nozzle210. A large number of extrusion holes 211 are made in the slopes 201a,as shown in FIG. 6. At an incline of to 30 degrees, however, no suchholes are necessary.

A pair of radiators 212 prevent both the body 201 and steel nozzle 210from overheating, nozzle 210 being disposed at the bottom of the body201 in such a manner that the melt 209 flowing down into the bottomsection can easily be extruded from the extrusion nozzle 210. The melt209 extruded from the nozzle 210 is rolled along upon the surfaces oftoothed rolls 213 deformed along the teeth due to the rolling effect,and securely clamped by the rolls 213. The rolls 213 are driven by amotor (not shown) at a predetermined speed to extrude a prescribedamount of melt 209 from the body 201. Water-cooled nozzles 215 arelocated right below nozzle 210 and spout out the cooled water to coolthe melt 209 rapidly and guide it into the section of contact betweenthe melt 209 and the rolls 213 while cooling the rolling surface by thegroove of the specific tooth form. More water-cooled nozzles 216 aredisposed underneath the rolls 213 to thereby provide for more rapidlycooling of the melt 209. The melt 209 so rolled is guided by the guiderolls 214 and extruded in the next process.

If the melt 209 has a poor degassing, the unmelted powder disposed abovethe gas collected everywhere on the surface and frequently falls down inthe body 201. As a result, a mixture of melt and non-melt is sometimesextruded from the bottom of the furnace body and sometimes thetemperature of the melt 209 is seriously affected thereby. Gas exhaustnozzle 220 is therefore made in the unmelted powder so as to remove theundesired gas before melting.

It should be noticed that the forced extrusion mechanism 213 of theinvention has a variety of toothed rolls 213a through 213f as shown byFIG. 7 through FIG. 11. Despite its rolling effect, the conventionalroll or caterpillar has no practical application as a mechanism forextruding the melt 209 at a predetermined speed in the relationshipbetween the amount of prepared melt and that of extruded melt. Thisinvention is capable of enhancing the rolling effect by the use of rollsor caterpillars of the specific tooth form, capable of effecting aforced extrusion, and capable of making the extrusion rate constant.

Several methods may be employed for breaking off the solidified melt.One method is to clamp the solidified melt between opposed clamps,denoted by numerals 300 in FIG. 16 and then when so held, strike thelower portion with a pneumatic hammer. Another way is to direct thesolidified column onto an inclined conveyor, such as conveyor 2200 inFIG. 6, the infeed end of the conveyor being disposed below rolls 214.

OPERATION On the foregoing description, the operation of the presentdevice should be apparent. The cup 90 is disposed over the protrudinglower end of the cooling sleeve 70. Also, the upper edge 73 of thecooling sleeve abutts the flange 28 of the furnace 20. Thereafter, rawmaterial, such as sand, silica, or other siliceous material is fed, byconveyor 116, into the bin 115, whence it passing down chute 114 andinto the interior of the body 21 and then moving downwardly through thecooling sleeve and collecting in the cup 90. The filling operation iscontinued until the cup 90, the sleeve, 70, and the furnace 20 arefilled with raw material A to the level indicated in FIG. 1.

Thereafter, an arc is struck between the electrodes 40 and the fusing ofthe siliceous material A is commenced. As the fusing continues, a globeG of melt is created which gradually grows in size, as more and more ofthe raw material A is converted into a molten viscous mass.

Periodically, the raw material will be bled from the bottom of thecolumn of raw material by the opening and closing of the gate valve,i.e. plate 97. This is illustrated in FIG. 13. As the globe G begins togrow, the gases created by the arc and by the vaporization of thesilica, create a chimney B in the molten material and in the rawmaterial A. These gases are taken off through the hood 1 10.

With continued periodic bleeding of the raw material from the bottomportion of the apparatus, and with continued growing of the globe due toadditional melting of raw material, the melt gradually flows through thethroat defined by lip 29 and eventually fills the annular space of thethroat so as to restrict any substantial flow of raw material throughthe throat. Furthermore, the raw material, which is disposed below theemerging column passing through the throat of lip 29, is essentiallyseparated from the raw material in the body 21. Thereafter, the rawmaterial captured below the lip 29 may be bled quite rapidly from theapparatus so as to create a condition such as illustrated in FIG. 15. Atthat time, there is no necessity for further use of the cup or cap 90and it may be lowered on the elevator and removed therefrom. Thus, theoperation is now in the condition shown in FIG. 15.

With continued operation, the column C protrudes lower and lower and isreceived on the elevator which, in turn, is lowered gradually to providesupport for this column C. After the raw material has been removed fromthe sleeve 90, the cooling water which is circulated therein, tends tocool and solidify the column C. As pointed out above when the column Chas been lowered sufficiently, it can be broken or severed, using anydesired method, such as the method described above. The passing of theexterior of the melt along the lip 29, tends to scrape the impuritiesfrom this surface and deposit the same along the inclined wall of bottom26. This permits a relatively pure product to be produced substantiallycontinuously. As the globe of melt grows, and ionization takes placewithin the interior, the electrodes may be withdrawn from each other soas to'create a more efficient arc. Furthermore, the raw material can befed gradually into the body 21 to make up for that material which hasbeen converted to a fused state.

It is therefore seen that the present apparatus and method enables asubstantially continuous operation. As the electrodes 40 begin to beused up, additional new electrodes may be screwed onto the threaded endsof the operating electrodes.

Periodically, of course, the operation must be shut down in order toclear out the impurities from along the bottom 26.

A better understanding of the present invention will be had by referenceto the following specific examples.

EXAMPLE I 30-ton of silica granules as the raw material for silicic acidwas fed into the body 201 through the hopper 202, the nozzle 210 beingclosed. An electric arc was then generated by electric citcuit throughthe electrode holders 207 to the prearranged 100-mm diameter bargraphite electrodes 205 and by adjusting the electrodeconveying devices208. The volumetric heat capacity due to the generation of an arc wasregulated by variation of the conductivity of the power supply (notshown) to varying the voltage. When conducting at 70 volts or less andin the range of 2,500 to 3,000 amperes for 10 min., there was gasgenerated between the two electrodes 205 thereby generating anapproximately spherical silicon-dioxide melt 209 around the gas D.

When continuously melting at 100 volts and 3,500 amperes while openingnozzle 210 to drop a suitable amount of unmelted raw material at propertimes, the melt 209 swelled in the lower part, as shown in FIG. 6. At150 volts and 4,000 amperes, the melt 209 continued to grow until itreached the nozzle 210. The nozzle 210 was left open in order tocontinuously extrude the melt 209. The melt 209 was more easily extrudedby flowing more rapidly, the unmelted raw material being interposedbetween the melt 209 and the slopes 2010 through nozzles 21 1.

In this way, the melt 209 was continuously extruded from the nozzles 210through the medium of the unmelted material, cooled by the coolingdevices 215, 216 to be solidified, and cut, being slightly supported onthe extruding devices 213, 214. The solidified por tions were thenfinely ground by the ordinary grinder into powdered fused silica aftercompletely removing the unmelted portions on the surface.

According to this invention, a considerably thick, large fused lump canbe obtained by continuously melt? ing while continuously feeding thepowdered material from the hopper and extruding it from the nozzleswhile melting. Furthermore, there is almost no mixture of melt andcarbon since the greater part of residual carbon contents generated byde-oxidation of the bar graphite electrodes is evaporated and removed inthe form of carbon dioxide (CO EXAMPLE II 3-ton of silica granules asraw material for silicic acid were first fed into the furnace body 201through the hopper 202 so as to be melted by an electric are generatedbetween the electrodes 205. When conducting at volts or less and 2,500amperes for about 10 minutes, an arc is generated, thereby forming aquasispherical melt 206 in the surroundings. While continuouslymelted atvolts and 3,500 amperes, the melt was made to grow gradually, bleedingthe optimum amount of powdered siliceous material from the bottom of thefurnace body. The melt 206 continues to flow downward and was extrudedfrom the extrusion nozzle 210 at the bottom of the body 201. The melt206 further flows down until it reaches a clamping position, where itwas clamped by the toothed rolls 209. At that instant, the melt 206 wascooled to such an extent that rolling was made impossible. It was,therefore, necessary to appreciably increase the voltage and current andmaintain the temperature as high as possible, as compared with thoseimmediately before extrusion of the melt 206 from the nozzle 210. Theoptimum amount of extruded melt 206 was 500 Kg/hr. The melt 206 wascontinuously extruded, regulating the rotation of the rolls 209 and 210by means of the stepless change gear so as to correspond to the amountof extrusion.

As previously described, the melt 206 was forcedly extruded according tothis invention, so as to form an almost unvarying quasi-sphereconsisting of melt and gas in the arc generating section, therebystabilizing the furnace situation and causing much less variation in thevoltage and current. The unmelted or semi-melted powder sticking to thesurface of the melt was removed by stretching the melt, resulting in abetter yield.

The contaminants or impurities in the melt tend to be cooler and collectalong the outer surface of the melt as the molten material flows throughthe main body 21 and the sleeve 70. When the melt begins to flow throughthe throat of lip 29, a seal is formed around the lip 29. The rate offlow is greater through the middle of the molten mass so that only therelatively pure molten silica flows for creating column C. Thedifferential movement of the contaminants and the pure molten silica isgreat enough to allow the resultant viscous flow to be free from theouter layer of contaminants. These contaminants are crystalline materialand collect along the bottom 26.

The above described invention provides many distinct advantages overprevious methods of producing fused silica. The first and probably mostimportant advantage of this invention is that a relatively pure fusedsilica product is formed. The product is substantially withoutcrystalline silica contaminants. Therefore, the product is ready to becrushed into grain fused silica without any further treatment to it. Asdescribed above, the contaminants that are present in the melt remain inthe body 21 as the melt is removed therefrom. The resultant dischargedmelt is almost all fused silica with no contaminant skin attached. Thisobviates the need for peeling the contaminant skin from the cooledsolidified melt.

Because almost no contaminants are present in the fused silica, thefused silica produced by this invention is more uniform and dense (i.e.,gas-free) than fused silica produced by the old methods. There isusually a five per cent increase in the average density of the improvedproduct, which is substantial for the silica art. The density of thefused silica more closely approaches the theoretical density of 2.2 thanpreviously produced fused silica. As is known, the greater the densityof the fused product, the greater the strength of the product.Therefore, a higher density is a much sought after advantage in thisart. The product from the present invention gives a 20,000 p.s.i.failure strength under compression vs. a 6,000 p.s.i. failure strengthunder compression for fused silica produced by the previous methods.

Also, the grain density of the product is uniformly higher with a rangeof 2.1 to 2.2 grams per cubic centimeter gm./c.c. as opposed to theprevious grain densi ty range of 2.0 to 2.1 grams/cc. and which has beenas low as 1.9 gm./c.c. The average grain density of the fused silicaproduced by this invention is 2.14 gm./c.c.

Because the production of the fused silica is a continuous process inthis invention and the apparatus is maintained in a relatively closedcondition, there is a conservation of the heat generated by theelectrical arc within the vessel 18 and less of a health hazzard. Thereis, therefore, a lower electrical power consumption by the electrodes50, per pound of glass produced due to this conservation of heat withinthe body 21. Also the amount of electrodes 48 consumed per pound ofglass produced is significantly reduced by this invention.

Another advantage of this invention over previous methods and apparatusfor the liquefaction or fusion of silica is an increased productionrate. An average of 1,000 lbs. per hour or more can be produced by thepresent invention as compared with an average of 600 pounds of fusedsilica perv hour with the old method and apparatus.

Another advantage is that the raw material is used only once in thisinvention instead of recycling the unused material as has been done inthe past. Since there is no recycling of the sand or rawmaterial thereis no concentration of impurities from the old sand, trapped with thenew sand, as in the old process. The present invention also lowers therate of raw material lost.

The invention also provides a labor saving method for the production offused silica. In the old method one man produced, on the average, 14pounds of fused silica per minute. With the present invention, the sameman can now produce a minimum of 15 pounds of fused silica per minute.

Finally, the invention provides an apparatus which requires lessmaintenance than previous devices. This is true because the body 21 doesnot have to be cleaned out as often as the devices did under the oldmethod of producing fused silica.

It is obvious that one skilled in the art may make modifications in thedetails of construction without departing from the spirit of theinvention which is set out in varying scope in the appended claims.

What is claimed is:

1. An apparatus for the continuous liquefaction of a finely dividedmaterial capable of forming a highly viscous material when heated to amolten condition, comprising a hollow vessel having a bottom openingtherein, means for introducing said finely divided material into saidvessel, heating means for generating sufficient heat within said vesselto continuously form said viscous material, receiving and bleeding meansdisposed below said bottom opening for receiving and intermittentlybleeding said finely divided material to start the continuous operationof said apparatus, said receiving and bleeding means including anopening therethrough aligned with said bottom opening and fixed relativethereto.

2. An apparatus as described in claim 1 wherein means are provided forcooling said vessel.

3. An apparatus as described in claim 1 wherein electrode feeding meansare operatively associated with said pair of electrodes for maintaininga preselected gap between said pair of electrodes.

4. An apparatus as described in claim 1 wherein said vessel includes amain body, an inwardly and downwardly sloping bottom connected to thelower end portion of said body, said opening being at the lower portionof said bottom and cooling means for applying a coolant adjacent saidbottom opening.

5. An apparatus as described in claim 3 wherein said electrode feedingmeans includes a movable carriage for each electrode, means on saidcarriage for securing said electrode to said carriage, tracks forsupporting said carriage and along which said carriage moves, and meansfor moving said carriage a predetermined distance along said track.

6. An apparatus as described in claim 1 including means disposed abovesaid vessel for feeding said finely divided material to said vessel.

7. An apparatus as described in claim 1 wherein said vessel furtherincludes a refractory ring on said bottom for defining said bottomopening.

8. An apparatus as described in claim 1 said support means includes anelevator disposed beneath said vessel for successively engaging andsupporting the lower portion of said viscous material as it flows fromsaid vessel.

9. The apparatus in claim 1, wherein said heating means includes a pairof electrodes within said vessel in opposed relationship to each otherfor providing an electrical arc therebetween.

10. The apparatus in claim 1, wherein said receiving and bleeding meansis removably attached to said vessel.

11. The apparatus in claim 1, wherein said receiving and bleeding meansincludes a sleeve having an axial opening therethrough, and furtherincludes means for temporarily stopping the flow of material throughsaid axial opening.

12. The apparatus in claim 1, wherein said receiving and bleeding meansincludes cooling means.

13. The apparatus in claim 12, wherein said cooling means includes apair of concentric hollow sleeves attached to each other and forming achamber therebetween.

14. The apparatus in claim 13, and further including means forcirculating a coolant through said chamber.

15. The apparatus in claim 14, wherein said coolant is water.

16. The apparatus in claim 11, wherein said means for stopping the flowis a cap removably attached to the lowermost end of said cooling means.

17. The apparatus in claim 16, wherein said cap includes a cup-shapedmember and a gate valve disposed in said cup-shaped member.

18. The apparatus in claim 1, and further including support meansdisposed below said cooling means for engaging and progressivelylowering a column of said viscous material from said vessel atsubstantially the same rate said viscous material is formed.

19. An apparatus as described in claim 18 wherein said support meansincludes a pair of opposed extruding rollers engaging opposite sides ofsaid column of viscous material.

20. An apparatus as described in claim 19 wherein said support meansfurther includes a pair of smoothsurfaced rollers disposed beneath saidextruding rollers and in alignment along said viscous material forguiding the water from said nozzles onto said viscous material.

21. An apparatus as described in claim 18 wherein said support meansincludes a conveyor disposed at an incline to said column of viscousmaterial.

22. A method for the continuous liquefaction of finely divided materialcapable of forming a highly viscous material when heated to a moltencondition, including the steps of:

introducing finely divided material into a hollow vessel having aconstricted bottom opening with a pair of electrodes within said vesselin opposed relationship to each other, providing an electrical arebetween said electrodes for generating sufficient heat to continuouslyform a globe of viscous material, removing a portion of said finelydivided material from below said viscous material to produce a column ofviscous material emerging from said opening, and thereafter periodicallyremoving thebottommost portion of said column.

23. The method in claim 22, and further including the step of coolingsaid viscous material after it flows from said vessel.

24. The method in claim 23, wherein the step of cooling includesapplying a cooling fluid directly to said viscous material.

25. The method in claim 23, wherein the step of cooling includescirculating a cooling fluid through a chamber that extends around saidviscous material.

26. An apparatus for the continuous liquefaction of finely dividedmaterial capable of forming a highly viscous material when heated to amolten condition, comprising a hollow vessel having a bottom openingtherein, means for temporarily closing said bottom opening, means forintroducing said finely divided material into said vessel, heating meansfor generating sufficient heat within said vessel to continuously formsaid viscous material, means for cooling said vessel, said cooling meansincluding a first cooling portion disposed around a portion of theexterior of said vessel, a second cooling portion extending around thebottom opening, and means for cooling said viscous material as it flowsfrom said vessel.

27. The apparatus in claim 26, wherein said heating means includes apair of electrodes within said vessel in opposed relationship to eachother for providing an electrical arc therebetween.

28. The apparatus in claim 26, wherein said first portion is a chambersurrounding said vessel.

29. The apparatus in claim 28, and further including means forcirculating a coolant through said chamber.

30. The apparatus in claim 29, wherein said coolant is water.

31. The apparatus in claim 26, wherein said second portion is a chambersurrounding said bottom opening.

32. The apparatus in claim 31, and further including means forcirculating a coolant through said chamber.

33. The apparatus in claim 32, wherein the coolant is water.

34. The apparatus in claim 26, wherein said means for cooling saidviscous material includes means for applying a cooling fluid directly tothe viscous material.

35. The apparatus in claim 26, wherein said means for cooling saidviscous material includes cooling means extending around said viscousmaterial.

36. An apparatus for the continuous liquefaction of finely dividedmaterial capable of forming a highly viscous material when heated tomolten condition, comprising a hollow vessel having a bottom openingtherein, means for temporarily closing said bottom opening, means forintroducing said finely divided material into said vessel, heating meansfor generating sufficient heat within said vessel to continuously formsaid viscous material, and support means for engaging and progressivelylowering a column of said viscous material from said vessel atsubstantially the same rate as said viscous material is formed, saidsupport means including an elevator disposed beneath said vessel forsuccessively engaging and supporting the lower portion of said viscousmaterial as it flows from said vessel.

37. The apparatus in claim 36, wherein said heating means includes apair of electrodes within said vessel in opposed relationship to eachother for providing an electrical arc therebetween.

38. An apparatus for the continuous liquefaction of finely dividedmaterial capable of forming a highly viscous material when heated to amolten condition, comprising a hollow vessel having a bottom openingtherein, means for temporarily closing said bottom opening, means forintroducing said finely divided material into said vessel, heating meansfor generating sufficient heat within said vessel to continuously formsaid viscous material, and means for applying a cooling fluid directlyto said viscous material as it flows from said vessel.

39. The apparatus in claim 38, wherein said heating means includes apair of electrodes within said vessel in opposed relationship to eachother for providing an electrical arc therebetween.

40. The device in claim 38, wherein the cooling fluid is water.

41. The device in claim 38, wherein said means includes a plurality ofnozzles disposed beneath the opening in the bottom of the furnace.

42. The device in claim 41, wherein a pair of toothed rolls is disposedbeneath said plurality of nozzles, and

further including means for clamping the melt between the rolls andturning the toothed rolls at a predetermined rate of speed.

43. The device in claim 42, wherein a second plurality of nozzles isdisposed beneath the toothed rolls for applying a cooling fluid directlyto the viscous material after it passes between the toothed rolls.

44. The device in claim 43, wherein a pair of rolls is disposed beneaththe second plurality of nozzles, and further including means forclamping the melt between the rolls and turning the rolls at apredetermined rate of speed.-

2. An apparatus as described in claim 1 wherein means are provided forcooling said vessel.
 3. An apparatus as described in claim 1 whereinelectrode feeding means are operatively associated with said pair ofelectrodes for maintaining a preselected gap between said pair ofelectrodes.
 4. An apparatus as describEd in claim 1 wherein said vesselincludes a main body, an inwardly and downwardly sloping bottomconnected to the lower end portion of said body, said opening being atthe lower portion of said bottom and cooling means for applying acoolant adjacent said bottom opening.
 5. An apparatus as described inclaim 3 wherein said electrode feeding means includes a movable carriagefor each electrode, means on said carriage for securing said electrodeto said carriage, tracks for supporting said carriage and along whichsaid carriage moves, and means for moving said carriage a predetermineddistance along said track.
 6. An apparatus as described in claim 1including means disposed above said vessel for feeding said finelydivided material to said vessel.
 7. An apparatus as described in claim 1wherein said vessel further includes a refractory ring on said bottomfor defining said bottom opening.
 8. An apparatus as described in claim1 said support means includes an elevator disposed beneath said vesselfor successively engaging and supporting the lower portion of saidviscous material as it flows from said vessel.
 9. The apparatus in claim1, wherein said heating means includes a pair of electrodes within saidvessel in opposed relationship to each other for providing an electricalarc therebetween.
 10. The apparatus in claim 1, wherein said receivingand bleeding means is removably attached to said vessel.
 11. Theapparatus in claim 1, wherein said receiving and bleeding means includesa sleeve having an axial opening therethrough, and further includesmeans for temporarily stopping the flow of material through said axialopening.
 12. The apparatus in claim 1, wherein said receiving andbleeding means includes cooling means.
 13. The apparatus in claim 12,wherein said cooling means includes a pair of concentric hollow sleevesattached to each other and forming a chamber therebetween.
 14. Theapparatus in claim 13, and further including means for circulating acoolant through said chamber.
 15. The apparatus in claim 14, whereinsaid coolant is water.
 16. The apparatus in claim 11, wherein said meansfor stopping the flow is a cap removably attached to the lowermost endof said cooling means.
 17. The apparatus in claim 16, wherein said capincludes a cup-shaped member and a gate valve disposed in saidcup-shaped member.
 18. The apparatus in claim 1, and further includingsupport means disposed below said cooling means for engaging andprogressively lowering a column of said viscous material from saidvessel at substantially the same rate said viscous material is formed.19. An apparatus as described in claim 18 wherein said support meansincludes a pair of opposed extruding rollers engaging opposite sides ofsaid column of viscous material.
 20. An apparatus as described in claim19 wherein said support means further includes a pair of smooth-surfacedrollers disposed beneath said extruding rollers and in alignment alongsaid viscous material for guiding the water from said nozzles onto saidviscous material.
 21. An apparatus as described in claim 18 wherein saidsupport means includes a conveyor disposed at an incline to said columnof viscous material.
 22. A method for the continuous liquefaction offinely divided material capable of forming a highly viscous materialwhen heated to a molten condition, including the steps of: introducingfinely divided material into a hollow vessel having a constricted bottomopening with a pair of electrodes within said vessel in opposedrelationship to each other, providing an electrical arc between saidelectrodes for generating sufficient heat to continuously form a globeof viscous material, removing a portion of said finely divided materialfrom below said viscous material to produce a column of viscous materialemerging from said opening, and thereafter periodically removing thebottommost portion of said column.
 23. The method in claim 22, andfurther including the step of Cooling said viscous material after itflows from said vessel.
 24. The method in claim 23, wherein the step ofcooling includes applying a cooling fluid directly to said viscousmaterial.
 25. The method in claim 23, wherein the step of coolingincludes circulating a cooling fluid through a chamber that extendsaround said viscous material.
 26. An apparatus for the continuousliquefaction of finely divided material capable of forming a highlyviscous material when heated to a molten condition, comprising a hollowvessel having a bottom opening therein, means for temporarily closingsaid bottom opening, means for introducing said finely divided materialinto said vessel, heating means for generating sufficient heat withinsaid vessel to continuously form said viscous material, means forcooling said vessel, said cooling means including a first coolingportion disposed around a portion of the exterior of said vessel, asecond cooling portion extending around the bottom opening, and meansfor cooling said viscous material as it flows from said vessel.
 27. Theapparatus in claim 26, wherein said heating means includes a pair ofelectrodes within said vessel in opposed relationship to each other forproviding an electrical arc therebetween.
 28. The apparatus in claim 26,wherein said first portion is a chamber surrounding said vessel.
 29. Theapparatus in claim 28, and further including means for circulating acoolant through said chamber.
 30. The apparatus in claim 29, whereinsaid coolant is water.
 31. The apparatus in claim 26, wherein saidsecond portion is a chamber surrounding said bottom opening.
 32. Theapparatus in claim 31, and further including means for circulating acoolant through said chamber.
 33. The apparatus in claim 32, wherein thecoolant is water.
 34. The apparatus in claim 26, wherein said means forcooling said viscous material includes means for applying a coolingfluid directly to the viscous material.
 35. The apparatus in claim 26,wherein said means for cooling said viscous material includes coolingmeans extending around said viscous material.
 36. An apparatus for thecontinuous liquefaction of finely divided material capable of forming ahighly viscous material when heated to molten condition, comprising ahollow vessel having a bottom opening therein, means for temporarilyclosing said bottom opening, means for introducing said finely dividedmaterial into said vessel, heating means for generating sufficient heatwithin said vessel to continuously form said viscous material, andsupport means for engaging and progressively lowering a column of saidviscous material from said vessel at substantially the same rate as saidviscous material is formed, said support means including an elevatordisposed beneath said vessel for successively engaging and supportingthe lower portion of said viscous material as it flows from said vessel.37. The apparatus in claim 36, wherein said heating means includes apair of electrodes within said vessel in opposed relationship to eachother for providing an electrical arc therebetween.
 38. An apparatus forthe continuous liquefaction of finely divided material capable offorming a highly viscous material when heated to a molten condition,comprising a hollow vessel having a bottom opening therein, means fortemporarily closing said bottom opening, means for introducing saidfinely divided material into said vessel, heating means for generatingsufficient heat within said vessel to continuously form said viscousmaterial, and means for applying a cooling fluid directly to saidviscous material as it flows from said vessel.
 39. The apparatus inclaim 38, wherein said heating means includes a pair of electrodeswithin said vessel in opposed relationship to each other for providingan electrical arc therebetween.
 40. The device in claim 38, wherein thecooling fluid is water.
 41. The device in claim 38, wherein said meansincludes a plurality of nozzles disposed beneath the openiNg in thebottom of the furnace.
 42. The device in claim 41, wherein a pair oftoothed rolls is disposed beneath said plurality of nozzles, and furtherincluding means for clamping the melt between the rolls and turning thetoothed rolls at a predetermined rate of speed.
 43. The device in claim42, wherein a second plurality of nozzles is disposed beneath thetoothed rolls for applying a cooling fluid directly to the viscousmaterial after it passes between the toothed rolls.
 44. The device inclaim 43, wherein a pair of rolls is disposed beneath the secondplurality of nozzles, and further including means for clamping the meltbetween the rolls and turning the rolls at a predetermined rate ofspeed.